Internet keeps dropping to the point I can't stream or have a meeting

I am at wits end with the wifi and internet here.  I am supposedly paying for 800, but when I run the Xfinity Speed Test, it says 95-100.  When I run the speed test from Speed Test dot net, it is 400. 

While watching television (apps through Roku as well as apps through my X1 box), the buffering and "check your internet connection" happen often enough we can't get through a show.  Last night we were able to watch but had trouble with the audio - which appears to be a network connection issue via searches.

I have been trying to log onto the gateway to run the diagnostics/get the info I have seen in other posts, and I cannot stay connected to the gateway long enough to get the info - whether wifi or wired, the connection drops.  When I tried the Xfinity Assistant troubleshooter, it says everything is fine and it's a problem with my laptop.  I really have zero idea where to go from here and cannot get anywhere with the assistant.  

I work remotely and this is affecting my ability to work.   Does anyone have any suggestions where I go from here?  I have NEVER been so unhappy with Xfinity as I have been these last few months.